Letter-Pairs Analysis is a free, web-based tool for calculating and visualizing the number of times a pair of letters appears in a given text. Each pair is represented as a 'bubble', sized according to how frequently that pair appears in the text. An HTML5 version is also now available. Note: this tool forms the basis of Voyant Bubbles.
Comments
The website cannot be found, but it can be seen from this webstie
https://web.archive.org/web/20060212183521/http://www.m-i-b.com.ar/mib/letter_pairs/eng/